Go Back  Bike Forums > Bike Forums > Electronics, Lighting, & Gadgets
Reload this Page >

Help with Cadence Sensor Magnet

Notices
Electronics, Lighting, & Gadgets HRM, GPS, MP3, HID. Whether it's got an acronym or not, here's where you'll find discussions on all sorts of tools, toys and gadgets.

Help with Cadence Sensor Magnet

Old 08-19-15, 03:08 PM
  #1  
LloydXmas
Newbie
Thread Starter
 
Join Date: Aug 2015
Posts: 4
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Help with Cadence Sensor Magnet

Hello all. I have a Trek Emonda that is outfitted with the Bontrager Duotrap speed and cadence sensor. I really like the sensor being tucked away into the frame but I am having one major problem. The slip on cadence magnet that slides on to the crank arm is stretched too far.

I have no problem getting it on but the rubber is stretched so much that it snaps in a week. After the first snap my LBS gave me a replacement, same kind, and it just did the same thing after another week. The magnet isn't contacting anything that would rip it off. I've been really watching for that.
It just seems that my Ultegra cranks are too wide for the rubber sensor magnet.

I tried placing a rare earth magnet on the inside of the crank, sticking it to the pedal's spindle, but it's too powerful and sets off both the cadence and speed parts of the sensor.

Can anyone recommend a solution or another magnet that anyone uses? The 10mm size was perfect distance but the rubber just want large enough for the crank. I'm looking for something that will be secure yet not something that will same the crank arm.

Thanks in advance.
LloydXmas is offline  
Old 08-19-15, 03:22 PM
  #2  
JohnJ80
Senior Member
 
Join Date: Feb 2011
Location: Minnesota
Posts: 4,187

Bikes: N+1=5

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 627 Post(s)
Liked 56 Times in 45 Posts
Originally Posted by LloydXmas View Post
Hello all. I have a Trek Emonda that is outfitted with the Bontrager Duotrap speed and cadence sensor. I really like the sensor being tucked away into the frame but I am having one major problem. The slip on cadence magnet that slides on to the crank arm is stretched too far.

I have no problem getting it on but the rubber is stretched so much that it snaps in a week. After the first snap my LBS gave me a replacement, same kind, and it just did the same thing after another week. The magnet isn't contacting anything that would rip it off. I've been really watching for that.
It just seems that my Ultegra cranks are too wide for the rubber sensor magnet.

I tried placing a rare earth magnet on the inside of the crank, sticking it to the pedal's spindle, but it's too powerful and sets off both the cadence and speed parts of the sensor.

Can anyone recommend a solution or another magnet that anyone uses? The 10mm size was perfect distance but the rubber just want large enough for the crank. I'm looking for something that will be secure yet not something that will same the crank arm.

Thanks in advance.

There is nothing nice you can say about the magnet approach. I just got rid of all of my magnets and went to the Wahoo Fitness RPM. It's an accelerometer based cadence device that is not much bigger than the stretch band magnet you are looking at and you don't need the receiver side. Never needs to be aligned with the sensor. Works fantastically well.

J.
JohnJ80 is offline  
Old 08-19-15, 03:31 PM
  #3  
LloydXmas
Newbie
Thread Starter
 
Join Date: Aug 2015
Posts: 4
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
I have a friend who has an accelerometer based sensor as well. But since I already have the receiver and something has to go on the crank arm anyway, I may as well have it be a cheap magnet rather than a whole new sensor.

Does anyone know if they make better sleeves or maybe one that relies on zip ties?
LloydXmas is offline  
Old 08-19-15, 03:36 PM
  #4  
JohnJ80
Senior Member
 
Join Date: Feb 2011
Location: Minnesota
Posts: 4,187

Bikes: N+1=5

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 627 Post(s)
Liked 56 Times in 45 Posts
Originally Posted by LloydXmas View Post
I have a friend who has an accelerometer based sensor as well. But since I already have the receiver and something has to go on the crank arm anyway, I may as well have it be a cheap magnet rather than a whole new sensor.

Does anyone know if they make better sleeves or maybe one that relies on zip ties?
Sure. I just finally got tired of having to align magnets everytime I bumped it which was pretty much everytime I took the bike off the top of the car.

Garmin has a zip tie one. $12. Lots of times your LBS will have a butt load of them laying around and just give you one.



J.
JohnJ80 is offline  
Old 08-19-15, 03:54 PM
  #5  
LloydXmas
Newbie
Thread Starter
 
Join Date: Aug 2015
Posts: 4
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Since the duotrap is in the frame, there's no issue of bumping it. And where the cadence magnet sits, I can't contact it with my foot at all. I've never had to readjust anything. I just need to replace the inferior magnet sleeve.
LloydXmas is offline  
Old 08-20-15, 07:35 AM
  #6  
Looigi
Senior Member
 
Looigi's Avatar
 
Join Date: Dec 2010
Posts: 8,950
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 12 Post(s)
Likes: 0
Liked 2 Times in 2 Posts
Get a 3x12mm or 1/8"x 1/2" rare earth magnet and stick it to the back of the crank arm with double stick tape or put it under a piece of gorilla tape. With duotrap, you're stuck with where the magnet has to go. With sensors that mount on the stay, you can often let the magnet stick to the inside end of the pedal spindle and align the sensor appropriately.
Looigi is offline  
Old 08-20-15, 08:10 AM
  #7  
JohnJ80
Senior Member
 
Join Date: Feb 2011
Location: Minnesota
Posts: 4,187

Bikes: N+1=5

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 627 Post(s)
Liked 56 Times in 45 Posts
Originally Posted by Looigi View Post
Get a 3x12mm or 1/8"x 1/2" rare earth magnet and stick it to the back of the crank arm with double stick tape or put it under a piece of gorilla tape. With duotrap, you're stuck with where the magnet has to go. With sensors that mount on the stay, you can often let the magnet stick to the inside end of the pedal spindle and align the sensor appropriately.

That's what I'd do. With the Duotrap arrangement, you might as well just stick the magnet down with double sided tape. You can find magnets of any size and shape on Amazon.

J.
JohnJ80 is offline  
Old 12-14-15, 09:53 AM
  #8  
afonge03
Newbie
 
Join Date: Dec 2015
Location: Philly
Posts: 1

Bikes: Trek FX 7.2

Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
I was having trouble with the cadence sensor and had to try a few different magnets so until I found one that was powerful enough to trip the cadence sensor without tripping the speed sensor. I finally went with these guys from Home Depot. I used one magnet attached to the magnet on the crank and used a strip of black electrical tape just to make sure it stays in place, but I honestly don't think I need it. Since then everything's been working fine.
Attached Images
File Type: jpg
bike mag.jpg (95.3 KB, 67 views)
afonge03 is offline  
Old 12-14-15, 04:05 PM
  #9  
John_V 
Senior Member
 
John_V's Avatar
 
Join Date: Jun 2011
Location: Tampa, Florida
Posts: 5,509

Bikes: 2017 Colnago C-RS, 2012 Colnago Ace, 2010 Giant Cypress hybrid

Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 381 Post(s)
Liked 75 Times in 54 Posts
The problem I think you'll have with crank magnets that attach with zip ties is slippage. I had a Cateye Double Wireless and used the magnet that came with it. It mounted nicely, but after riding on rough roads, the vibration would cause it to slide down to the bottom of crank, no matter how tight the ties were. I now use a rare earth magnet on the pedal with my sensor mounted on the stay. The Duotraps are nice but don't give you much wiggle room for the magnet positions.

My suggestion would be to search the different manufacturers web sites and look in their computer accessories for a cadence magnet type that might work for you.
__________________
HCFR Cycling Team
Ride Safe ... Ride Hard ... Ride Daily

2017 Colnago C-RS
2012 Colnago Ace
2010 Giant Cypress
John_V is offline  
Old 12-14-15, 04:33 PM
  #10  
Seattle Forrest
Senior Member
 
Seattle Forrest's Avatar
 
Join Date: Mar 2010
Location: Seattle, WA
Posts: 21,221
Mentioned: 67 Post(s)
Tagged: 0 Thread(s)
Quoted: 12049 Post(s)
Liked 3,407 Times in 1,899 Posts
I would probably just use tape.
Seattle Forrest is offline  
Old 12-14-15, 04:52 PM
  #11  
JohnJ80
Senior Member
 
Join Date: Feb 2011
Location: Minnesota
Posts: 4,187

Bikes: N+1=5

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 627 Post(s)
Liked 56 Times in 45 Posts
Originally Posted by John_V View Post
The problem I think you'll have with crank magnets that attach with zip ties is slippage. I had a Cateye Double Wireless and used the magnet that came with it. It mounted nicely, but after riding on rough roads, the vibration would cause it to slide down to the bottom of crank, no matter how tight the ties were. I now use a rare earth magnet on the pedal with my sensor mounted on the stay. The Duotraps are nice but don't give you much wiggle room for the magnet positions.

My suggestion would be to search the different manufacturers web sites and look in their computer accessories for a cadence magnet type that might work for you.
Reason #93 to move to accelerometer based sensors. No magnet alignment issues anymore.

J.
JohnJ80 is offline  
Old 12-15-15, 07:03 PM
  #12  
John_V 
Senior Member
 
John_V's Avatar
 
Join Date: Jun 2011
Location: Tampa, Florida
Posts: 5,509

Bikes: 2017 Colnago C-RS, 2012 Colnago Ace, 2010 Giant Cypress hybrid

Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 381 Post(s)
Liked 75 Times in 54 Posts
Originally Posted by JohnJ80
Reason #93 to move to accelerometer based sensors. No magnet alignment issues anymore.

J.
Since I use my phone with a RFLKT and BT sensors the only BT based accelerometer available is the Wahoo RPM but that still leaves a magnetic speed sensor that I have to have. Luckily, I've not had any alignment issues because my bike is transported on a fork mount so I don't get the sensor bumped like you would on a trunk or hitch mount. Right now, the only time I have to align my sensor to the magnets is when I change the sensor battery.
__________________
HCFR Cycling Team
Ride Safe ... Ride Hard ... Ride Daily

2017 Colnago C-RS
2012 Colnago Ace
2010 Giant Cypress
John_V is offline  
Old 12-16-15, 09:27 AM
  #13  
JohnJ80
Senior Member
 
Join Date: Feb 2011
Location: Minnesota
Posts: 4,187

Bikes: N+1=5

Mentioned: 20 Post(s)
Tagged: 0 Thread(s)
Quoted: 627 Post(s)
Liked 56 Times in 45 Posts
Originally Posted by John_V View Post
Since I use my phone with a RFLKT and BT sensors the only BT based accelerometer available is the Wahoo RPM but that still leaves a magnetic speed sensor that I have to have. Luckily, I've not had any alignment issues because my bike is transported on a fork mount so I don't get the sensor bumped like you would on a trunk or hitch mount. Right now, the only time I have to align my sensor to the magnets is when I change the sensor battery.
You must have better luck than I. I don't put my bikes in the car but they go on hitch racks either on the back or on top. Either the magnet gets turned on the spoke or the sensor gets bumped somehow and they are out of alignment. Then multiply by both my wife's bikes and mine. The way you find out it's a problem when it malfunctions when you start riding. Then you have to stop, re-align, spin the wheel and verify. It's a pain.

Either way, probably within the next year, two at the most, with the steep drop in price of the actual accelerometer part thanks to smartphone volumes, you are going to to see the magnetic sensors go away anyhow. A very good thing.

There are several sensors that are in final testing now. I'm surprised that Wahoo hasn't announced one, it's got to be minor reprogramming on the cadence sensor they already have. I'm betting one shows up in time to ride with this spring.

J.
JohnJ80 is offline  
Old 12-16-15, 10:00 AM
  #14  
Seattle Forrest
Senior Member
 
Seattle Forrest's Avatar
 
Join Date: Mar 2010
Location: Seattle, WA
Posts: 21,221
Mentioned: 67 Post(s)
Tagged: 0 Thread(s)
Quoted: 12049 Post(s)
Liked 3,407 Times in 1,899 Posts
Originally Posted by John_V View Post
Since I use my phone with a RFLKT and BT sensors the only BT based accelerometer available is the Wahoo RPM but that still leaves a magnetic speed sensor that I have to have. Luckily, I've not had any alignment issues because my bike is transported on a fork mount so I don't get the sensor bumped like you would on a trunk or hitch mount. Right now, the only time I have to align my sensor to the magnets is when I change the sensor battery.
The only time I've ever had magnet alignment issues is when I've kicked the s/c sensor with my heel. You're right, battery changes too. Transport my bike in the car a lot. It's just never been an issue.

I got rid of the sensor when I got a power meter, and use GPS for speed. At the end of the day if the ride distance is off by 50 feet per mile it won't affect anything.
Seattle Forrest is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
ZapoTeX
Electronics, Lighting, & Gadgets
9
04-26-19 05:54 PM
GiantTCR
Electronics, Lighting, & Gadgets
5
07-23-15 11:00 AM
bigredkevbot
Bicycle Mechanics
7
01-20-15 12:07 PM
mattkime
Bicycle Mechanics
0
07-22-12 06:12 PM
sirious94
Road Cycling
2
03-10-10 07:38 AM

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.